[PATCH 1/3] drm/xe/query: Increase timestamp width

[Lucas De Marchi]

On Wed, Oct 09, 2024 at 08:48:45PM -0700, Lucas De Marchi wrote:
>Starting with Xe2 the timestamp is a full 64 bit counter, contrary to
>the 36 bit that was available before. Although 36 should be sufficient
>for any reasonable delta calculation (for Xe2, of about 30min), it's
>surprising to userspace to get sommething truncated. Also if the
>timestamp being compared to is coming from the GPU and the application
>is not careful enough to apply the width there, a delta calculation
>would be wrong.
>
>Extend it to full 64-bits for non-media engines starting with Xe2.
>
>Bspec: 60411
>Cc: Szymon Morek <szymon.morek at intel.com>
>Signed-off-by: Lucas De Marchi <lucas.demarchi at intel.com>
>---
> drivers/gpu/drm/xe/xe_query.c | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
>diff --git a/drivers/gpu/drm/xe/xe_query.c b/drivers/gpu/drm/xe/xe_query.c
>index 158629971eab3..a1f4cc25bea68 100644
>--- a/drivers/gpu/drm/xe/xe_query.c
>+++ b/drivers/gpu/drm/xe/xe_query.c
>@@ -164,7 +164,11 @@ query_engine_cycles(struct xe_device *xe,
> 			  cpu_clock);
>
> 	xe_force_wake_put(gt_to_fw(gt), XE_FORCEWAKE_ALL);
>-	resp.width = 36;
>+
>+	if (!xe_gt_is_media_type(gt) && GRAPHICS_VER(xe) >= 20)

I sent this to follow the spec to the letter, but I'm thinking the spec
is not tagged correctly here.... the counter is the same, replicated to
all engines. It doesn't make sense to be different in the media gt.

In fact, testing on LNL:

$ sudo ./build/tools/intel_reg read 0x2358 0x235c 0x1c0358 0x1c035c
Opened device: /dev/dri/card0
                                     (0x00002358): 0x52d026c7
                                     (0x0000235c): 0x00000062
                                     (0x001c0358): 0x52d027b3
                                     (0x001c035c): 0x00000062

So... the upper word returns the same thing for both rcs and vcs and
it's > 36b.

+Matt Roper as he understand the spec tagging. Maybe I read it wrong.

It would be good if we don't have to differentiate the width based on
gt.


Lucas De Marchi

>+		resp.width = 64;
>+	else
>+		resp.width = 36;
>
> 	/* Only write to the output fields of user query */
> 	if (put_user(resp.cpu_timestamp, &query_ptr->cpu_timestamp))
>-- 
>2.46.2
>